id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
514792972,MDU6SXNzdWU1MTQ3OTI5NzI=,3470,warn when updating coord.values : indexes are not updated,35295222,closed,0,,,7,2019-10-30T16:05:14Z,2020-03-23T13:42:50Z,2020-03-23T13:42:50Z,NONE,,,,"Hi, I've recently come across what it seems to be a bit annoying bug. After adding an offset to the time dimension using pd.add_offset(), the wrong times are selected when using .sel(). I've come across this behavior in recent versions of xarray, starting from 0.12. I've now worked around it by using ds.assign_coords(time = ...). I'm not sure however if this is a possible bug in Xarray or Pandas. Below a minimum working example.

#### MCVE Code Sample
<!-- In order for the maintainers to efficiently understand and prioritize issues, we ask you post a ""Minimal, Complete and Verifiable Example"" (MCVE): http://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports -->

```python
import xarray as xr
import pandas as pd
import numpy as np

temp = 15 + 8 * np.random.randn(2, 2, 3)
lon = [[-99.83, -99.32], [-99.79, -99.23]]
lat = [[42.25, 42.21], [42.63, 42.59]]
ds = xr.Dataset({'temperature': (['x', 'y', 'time'],  temp)},
                 coords={'lon': (['x', 'y'], lon),
                         'lat': (['x', 'y'], lat),
                         'time': pd.date_range('2014-09-01', periods=3,freq='MS'),
                         })

seltime = ds.time[2]
ds.time.values = pd.to_datetime(ds.time.values) + pd.DateOffset(months=2)
```
```python
print(ds.sel(time=seltime).time)
```
```python
<xarray.DataArray 'time' ()>
array('2015-01-01T00:00:00.000000000', dtype='datetime64[ns]')
Coordinates:
    time     datetime64[ns] 2015-01-01
```
```python
print(seltime)
```
```python
<xarray.DataArray 'time' ()>
array('2014-11-01T00:00:00.000000000', dtype='datetime64[ns]')
Coordinates:
    time     datetime64[ns] 2014-11-01
```



#### Expected Output
Expected output is that seltime and ds.sel(time=seltime).time are the same


#### Output of ``xr.show_versions()``
<details>
# Paste the output here xr.show_versions() here
INSTALLED VERSIONS
------------------
commit: None
python: 3.7.3 (default, Apr  3 2019, 19:16:38) 
[GCC 8.0.1 20180414 (experimental) [trunk revision 259383]]
python-bits: 64
OS: Linux
OS-release: 4.15.0-58-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8
libhdf5: 1.10.0
libnetcdf: 4.6.0

xarray: 0.14.0
pandas: 0.25.2
numpy: 1.17.3
scipy: 1.3.1
netCDF4: 1.4.0
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: 1.0.3.4
nc_time_axis: 1.1.0
PseudoNetCDF: None
rasterio: 1.0.26
cfgrib: None
iris: None
bottleneck: 1.2.1
dask: 2.3.0
distributed: None
matplotlib: 3.1.1
cartopy: 0.17.0
seaborn: 0.9.0
numbagg: None
setuptools: 41.2.0
pip: 9.0.1
conda: None
pytest: None
IPython: 7.7.0
sphinx: None
</details>
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